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Title: Aerosol properties computed from aircraft-based observations during the ACE-Asia campaign: 2. A case study of lidar ratio closure

Abstract

For a vertical profile with three distinct layers (marine boundary, pollution and dust layers), observed during the ACE-Asia campaign, we carried out a comparison between the modeled lidar ratio vertical profile and that obtained from co-located airborne NASA AATS-14 sunphotometer and shipborne Micro-Pulse Lidar (MPL) measurements. The vertically resolved lidar ratio was calculated from two size distribution vertical profiles – one obtained by inversion of sunphotometer-derived extinction spectra, and one measured in-situ – combined with the same refractive index model based on aerosol chemical composition. The aerosol model implies single scattering albedos of 0.78 – 0.81 and 0.93 – 0.96 at 0.523 μm (the wavelength of the lidar measurements), in the pollution and dust layers, respectively. The lidar ratios calculated from the two size distribution profiles agree closely in the dust layer; they are however, significantly lower than the lidar ratios derived from combined lidar and sunphotometer measurements. Uncertainties in aerosol size distributions and refractive index only partly explain these differences, suggesting that particle nonsphericity in this layer is an additional explanation. In the pollution layer, the two size distribution profiles yield lidar ratios that agree within the estimated uncertainties. The retrieved size distributions result in a lidar ratio whichmore » is in closer agreement with that derived from lidar/sunphotometer measurements in this layer, with still large differences at certain altitudes (the largest relative difference was 46%). We explain these differences by non-uniqueness of the result of the size distribution retrieval, by a lack of information on the mixing state of particles, and the vertical variability of the particle refractive index.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
902039
Report Number(s):
PNNL-SA-54428
Journal ID: ISSN 0278-6826; ASTYDQ; TRN: US200716%%600
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Aerosol Science and Technology, 41(3):231-243; Journal Volume: 41; Journal Issue: 3
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; AEROSOLS; CHEMICAL COMPOSITION; CLOSURES; DISTRIBUTION; DUSTS; NASA; OPTICAL RADAR; POLLUTION; REFRACTIVE INDEX; SCATTERING; SPECTRA; WAVELENGTHS

Citation Formats

Kuzmanoski, Maja, Box, M. A., Schmid, Beat, Box, G. P., Wang, Jian, Russel, P. R., Bates, D., Jonsson, Haf, Welton, E. J., and Seinfeld, J. H. Aerosol properties computed from aircraft-based observations during the ACE-Asia campaign: 2. A case study of lidar ratio closure. United States: N. p., 2007. Web. doi:10.1080/02786820601146977.
Kuzmanoski, Maja, Box, M. A., Schmid, Beat, Box, G. P., Wang, Jian, Russel, P. R., Bates, D., Jonsson, Haf, Welton, E. J., & Seinfeld, J. H. Aerosol properties computed from aircraft-based observations during the ACE-Asia campaign: 2. A case study of lidar ratio closure. United States. doi:10.1080/02786820601146977.
Kuzmanoski, Maja, Box, M. A., Schmid, Beat, Box, G. P., Wang, Jian, Russel, P. R., Bates, D., Jonsson, Haf, Welton, E. J., and Seinfeld, J. H. Tue . "Aerosol properties computed from aircraft-based observations during the ACE-Asia campaign: 2. A case study of lidar ratio closure". United States. doi:10.1080/02786820601146977.
@article{osti_902039,
title = {Aerosol properties computed from aircraft-based observations during the ACE-Asia campaign: 2. A case study of lidar ratio closure},
author = {Kuzmanoski, Maja and Box, M. A. and Schmid, Beat and Box, G. P. and Wang, Jian and Russel, P. R. and Bates, D. and Jonsson, Haf and Welton, E. J. and Seinfeld, J. H.},
abstractNote = {For a vertical profile with three distinct layers (marine boundary, pollution and dust layers), observed during the ACE-Asia campaign, we carried out a comparison between the modeled lidar ratio vertical profile and that obtained from co-located airborne NASA AATS-14 sunphotometer and shipborne Micro-Pulse Lidar (MPL) measurements. The vertically resolved lidar ratio was calculated from two size distribution vertical profiles – one obtained by inversion of sunphotometer-derived extinction spectra, and one measured in-situ – combined with the same refractive index model based on aerosol chemical composition. The aerosol model implies single scattering albedos of 0.78 – 0.81 and 0.93 – 0.96 at 0.523 μm (the wavelength of the lidar measurements), in the pollution and dust layers, respectively. The lidar ratios calculated from the two size distribution profiles agree closely in the dust layer; they are however, significantly lower than the lidar ratios derived from combined lidar and sunphotometer measurements. Uncertainties in aerosol size distributions and refractive index only partly explain these differences, suggesting that particle nonsphericity in this layer is an additional explanation. In the pollution layer, the two size distribution profiles yield lidar ratios that agree within the estimated uncertainties. The retrieved size distributions result in a lidar ratio which is in closer agreement with that derived from lidar/sunphotometer measurements in this layer, with still large differences at certain altitudes (the largest relative difference was 46%). We explain these differences by non-uniqueness of the result of the size distribution retrieval, by a lack of information on the mixing state of particles, and the vertical variability of the particle refractive index.},
doi = {10.1080/02786820601146977},
journal = {Aerosol Science and Technology, 41(3):231-243},
number = 3,
volume = 41,
place = {United States},
year = {Tue Apr 03 00:00:00 EDT 2007},
month = {Tue Apr 03 00:00:00 EDT 2007}
}
  • In this paper aerosol size distributions retrieved from aerosol layer optical thickness spectra, derived from the 14-channel NASA Ames Airborne Tracking Sunphotometer (AATS-14) measurements during the ACE-Asia campaign, are presented. Focusing on distinct aerosol layers (with different particle characteristics) observed in four vertical profiles, we compare the results of two different retrieval methods: constrained linear inversion and a non-linear least squares method. While the former does not use any assumption about the analytical form of the size distribution, the latter was used to retrieve parameters of a bimodal lognormal size distribution. Furthermore, comparison of the retrieved size distributions with thosemore » measured in-situ, aboard the same aircraft on which the sunphotometer was flown, was carried out. Results of the two retrieval methods showed good agreement in the radius ranges from ~0.1μm to ~1.2-2.0μm, close to the range of retrievable size distributions from the AATS-14 measurements. In this radius interval, shapes of retrieved and measured size distributions were similar, in accord with close wavelength dependencies of the corresponding optical thicknesses. Additionally, the effect of a size-resolved refractive index on the retrieved size spectra was investigated in selected cases. Retrieval using a constant refractive index pertaining to particle sizes within the range of retrievable size distributions resulted in a size distribution very close to the one retrieved using a size-resolved refractive index.« less
  • Aerosol chemical composition, size distributions, and optical properties were measured during 17 aircraft flights in New England and Middle Atlantic States as part of the summer 2002 NEAQS field campaign. An Aerodyne Aerosol Mass Spectrometer (AMS) was operated with a measurement cycle of 30 s, about an order of magnitude faster than used for ground-based measurements. Noise levels within a single measurement period were sub μg m-3. Volume data derived from the AMS were compared with volume measurements from a PCASP optical particle detector and an Scanning Mobility Particle Spectrometer (SMPS); calculated light scattering was compared with measured values frommore » an integrating nephelometer. The median ratio for AMS/SMPS volume was 1.25; the median ratio for AMS/nephelometer scattering was 1.18. Size spectra were compared for subsets of samples with different effective diameters (Deff). There is good agreement between the AMS, PCASP, and SMPS spectra for larger values of Deff but an unexplained over-prediction in the AMS for small values. A dependence of the AMS collection efficiency on aerosol acidity was quantified by a comparison between AMS and PCASP volumes in 2 high sulfate plumes. Average aerosol concentrations were 11 μg m-3. The organic content was high in comparison to monitoring data from the IMPROVE network, varying from 70% in clean air to 40% in high concentration sulfate plumes. The ratio of organic aerosol to CO and light absorption acting were examined as a function of photochemical age. CO is a conservative tracer for urban emissions and light absorption is a surrogate for black carbon which is also conservative. Comparisons were made to surface ratios measured under conditions where there is little secondary organic aerosol (SOA). An increase in these ratios relative to surface values indicates that 70 - 80% of the organic aerosol in polluted air masses was secondary. Most of this SOA is rapidly formed within a few hours. At longer time scales there is a slow accumulation of organic aerosol and a slow increase in light absorption per unit mass of black carbon. Our results demonstrate the utility of the AMS as a rapid response instrument suitable for aircraft operations.« less
  • Measurements of aerosol properties from aircraft, satellite and ground-based remote sensing: A case study from the Dust and Biomass burning Experiment (DABEX)
  • We present modeled aerosol optical properties (single scattering albedo, asymmetry parameter, and lidar ratio) in two layers with different aerosol loadings and particle sizes, observed during the Southern African Regional Science Initiative 2000 (SAFARI 2000) campaign. The optical properties were calculated from aerosol size distributions retrieved from aerosol layer optical thickness spectra, measured using the NASA Ames airborne tracking 14-channel sunphotometer (AATS-14) and the refractive index based on the available information on aerosol chemical composition. The study focuses on sensitivity of modeled optical properties in the 0.3–1.5 μm wavelength range to assumptions regarding the mixing scenario. We considered two modelsmore » for the mixture of absorbing and nonabsorbing aerosol components commonly used to model optical properties of biomass burning aerosol: a layered sphere with absorbing core and nonabsorbing shell and the Maxwell–Garnett effective medium model. In addition, comparisons of modeled optical properties with the measurements are discussed. We also estimated the radiative effect of the difference in aerosol absorption implied by the large difference between the single scattering albedo values (~0.1 at midvisible wavelengths) obtained from different measurement methods for the case with a high amount of biomass burning particles. For that purpose, the volume fraction of black carbon was varied to obtain a range of single scattering albedo values (0.81–0.91 at λ=0.50 μm). Finally, the difference in absorption resulted in a significant difference in the instantaneous radiative forcing at the surface and the top of the atmosphere (TOA) and can result in a change of the sign of the aerosol forcing at TOA from negative to positive.« less
  • Upcoming multiyear satellite lidar aerosol observations need strong support by a worldwide ground-truth lidar network. In this context the question arises as to whether the ground stations can deliver the same results as obtained from space when the Klett formalism is applied to elastic backscatter lidar data for the same aerosol case. This question is investigated based on simulations of observed cases of simple and complex aerosol layering. The results show that the differences between spaceborne and ground-based observations can be as large as20% for the backscatter and extinction coefficients and the optimum estimates of the column lidar ratios. Inmore » cases with complex aerosol layering, the application of the two-layer approach can lead to similar results (space, ground) and accurate products provided that horizontally homogeneous aerosol conditions are given.« less